ANCHORAGE, Alaska -- A petition seeking Endangered Species Act protection for a rare loon that breeds in Alaska's National Petroleum Reserve has been accepted for review by the U.S. Fish and Wildlife Service.

Conservationists hope an eventual listing of the yellow-billed loon will curb petroleum development in the 23-million acre reserve that covers much of Alaska's western North Slope.

The petition was filed three years ago by the Center for Biological Diversity, the National Resource Defense Council, Pacific Environment and other U.S. and Russian scientific and conservation organizations.

The Fish and Wildlife Service said it will publish its determination Wednesday in the Federal Register that the yellow-billed loon may merit protections.

The finding requires the agency to solicit public comment, carry out a status review of the species, and if merited, issue a proposed rule to protect the loons later this year.

The yellow-billed loon breeds in tundra wetlands in Alaska, Canada and Russia, and winters along the west coasts of Canada and the United States.

Petroleum development through leasing ordered by President Bush could reduce its numbers, said Brendan Cummings, ocean program director at the Center for Biological Diversity.

"The yellow-billed loon is one of the rarest and most vulnerable birds in the United States, yet the Bush administration's plan to 'protect' it is to approve oil drilling in its habitat," Cummings said.

The Fish and Wildlife Service estimates there are 16,500 yellow-billed loons in the world, including 3,700 to 4,900 that breed in Alaska. More than 75 percent of the Alaska breeders nest in the petroleum reserve. Smaller numbers breed on the Seward Peninsula and on St. Lawrence Island.

President Warren Harding created the National Petroleum Reserve-Alaska in 1923 as an emergency oil supply for the Navy. Current leasing plans come from a presidential directive guiding the Department of the Interior to foster oil and gas development there.

The Bureau of Land Management two weeks ago halted planning efforts for oil and gas development in the 9.2-million acre Southern Planning area, one of three planning areas, due to public opposition and the impracticality of development. The southern area is the primary calving area for the Western Arctic Caribou Herd.

According to the Fish and Wildlife Service, yellow-billed loons nest exclusively in coastal and low-lying Arctic tundra, always near permanent, fish-bearing lakes.

The large-bodied birds have low reproductive success and depend on high annual adult survival to maintain population levels. Individual birds must live many years before they can reliably replace themselves with offspring that survive long enough to breed, according to the agency.

The agency's finding, called a 90-day finding despite the filing of the original petition in March 2004, is based on scientific information provided by the conservation groups.

They cite threats including destruction and modification of habitat due to development and pollution and lack of regulatory protection.

Birds that breed in Alaska spend winters off the coast of Russia and face drowning in fishing nets, plus threats from petroleum development in the Sea of Okhotsk, Cummings said.

Yellow-billed loons do not recover easily from population declines, are susceptible to disturbance and may be vulnerable to habitat loss, according to the Fish and Wildlife Service.

Inundation of their freshwater breeding areas by saltwater levels rising because of global warming is another threat, Cummings said. However, oil and gas development in nesting areas is foremost in the petitioners' minds.

"Industrializing the Arctic is not the way to protect a rare bird," he said.